# Creating the Graph Point Data

Autocad AddLightWeightPolyline method requires an array of doubles. It does not require the lowerbound of the array to be zero. An array simply has to have an even number of elements, one element for each X and each Y alternating. (x1, y1, x2, y2, x3, y3…) For indexes and loops I typically use the counting numbers, which do not include zero. I am evaluating an autocad work-alike program that is similar but requires arrays to be zero-based. It does not throw an error with a one-based array but results are a failure. it creates zero values for non-existent indexes that it expects. However there is no reason the arrays cannot be zero-based so they run in both packages. To that end for that reason i am re-doing the graph loops.

Only the array needs to be zero based. The loop still executes one time for each point. The index of the array starts with zero.

Calculation of points for Coordinate XY graphing –

Autocad does not care what indexes the array pt (below) was created with. The work-alike absolutely requires a starting index of zero.

```Dim plineobj As AcadLWPolyline
```

in line drawing mode, subtracting lbound from ubound adding one and dividing by two will give the number of points in the array. There is one less line. Since we know lbound is zero we could remove that. The loop iterates once for each line drawn. We could do the loop to handle any lbound value, but it would be a little messy with no immediate benefit. For now we expect a zero base array.

```Sub draw_lines(ByRef pt() As Double)
Dim i As Integer, numpts As Integer, numlines As Integer
Dim x1 As Double, x2 As Double, y1 As Double, y2 As Double
Dim pt1(0 To 2) As Double
Dim pt2(0 To 2) As Double

numpts = (UBound(pt) - LBound(pt) + 1) / 2
numlines = numpts - 1

'this requires a zero base array
For i = 1 To numlines
x1 = pt(i * 2 - 2)
y1 = pt(i * 2 - 1)
x2 = pt(i * 2)
y2 = pt(i * 2 + 1)

pt1(0) = x1: pt1(1) = y1: pt1(2) = 0
pt2(0) = x2: pt2(1) = y2: pt2(2) = 0

Next i

Update
End Sub
```

Lines w/limits mode we use when the Y value approaches infinity, such as y=1/x near x=0. It is otherwise the same.

```Sub draw_lines_wlimits(xlim As Double, ylim As Double, ByRef pt() As Double)
Dim i As Integer, numpts As Integer, numlines As Integer
Dim x1 As Double, x2 As Double, y1 As Double, y2 As Double
Dim pt1(0 To 2) As Double
Dim pt2(0 To 2) As Double

numpts = (UBound(pt) - LBound(pt) + 1) / 2
numlines = numpts - 1

'this requires a zero base array
For i = 1 To numlines
x1 = pt(i * 2 - 2)
y1 = pt(i * 2 - 1)
x2 = pt(i * 2)
y2 = pt(i * 2 + 1)

If Abs(x1) < xlim And Abs(y1) < ylim And Abs(x2) < xlim And Abs(y2) < ylim Then
pt1(0) = x1: pt1(1) = y1: pt1(2) = 0
pt2(0) = x2: pt2(1) = y2: pt2(2) = 0
End If
Next i

Update
End Sub
```

point mode

```
Sub draw_points(ByRef pt() As Double)
Call pointmode
Dim i As Integer, numpts As Integer
Dim x1 As Double, y1 As Double

Dim pt1(0 To 2) As Double
numpts = (UBound(pt) - LBound(pt) + 1) / 2

'this requires a zero base array
For i = 1 To numpts
x1 = pt(i * 2 - 2)
y1 = pt(i * 2 - 1)
pt1(0) = x1: pt1(1) = y1: pt1(2) = 0